In weaving, warp yarns are subjected to various forces and undergo complex deformation. From the basic movement of the loom:
(1) In the opening movement, the warp yarn is bent into a broken line at the eye of the heald by the roughly straight heald line, which extends in proportion to the square of the shed height. At the same time, due to the length asymmetry between the front and back of the shed, the warp slips in the heald eye and produces friction. When the upper and lower warps rise and fall alternately in the opening movement, intense friction occurs between them.
(2) In the weft insertion movement, the shuttle of the shuttle loom relies on the shed and runs through it with friction, especially when entering and leaving the shed, the warp yarn of the side is squeezed to a great extent, resulting in bending, elongation and friction. The weft guide parts of the shuttleless loom also have considerable friction on the warp yarn.
(3) In beating motion, the warp yarn in front of the shed is subject to the friction of the sley in reciprocating motion. The squeeze friction between the reed and the edge warp is more intense because of the shrinkage. In the weft beading zone, the back and forth movement caused by each beading will increase the friction between warp and heald eye.
(4) In let-off and coiling movement, there is always a certain brake tension when the warp is sent out on the weaving shaft. Most of the existing let-off mechanisms belong to tension adjusting let-off mechanisms, and the let-off amount is controlled by the sensor feedback of warp tension. Therefore, when the warp yarn with weak knots passes through the back beam, it begins to break. The winding movement will also affect the warp tension, and form the warp elastic-plastic deformation system with let-off, beating and opening.
Thus it can be seen that the forces and deformations borne by warp yarn during weaving are mainly formed by tension (which requires no breakage), elongation (which can be recovered by cyclic deformation) and friction (which does not wool, pilling or wear off).
At the same time, it is worth paying attention to the hairiness problem. In the opening of warp yarn, the hairiness stretched out will entangle each other, making the opening unclear, causing difficult to eliminate the defects such as jumping yarn, jumping flower and hanging warp. In the weft insertion of air jet loom, the weft blocking caused by unclear opening is the main factor affecting efficiency. So hair reduction is an important indicator.
In view of the above situation, in order to improve the warp weaving performance, the effective method adopted in the weaving preparation engineering is sizing. That is, the size of adhesive material as the main body of the warp is applied to the surface of the warp to a certain depth, and the size structure of the pulp and yarn is formed after drying.
After sizing, the warp performance should be enhanced, elongation, wear resistance, hair sticking. Filament by sizing, so that single silk mutual adhesion, with a cluster, to prevent wire hair or broken, and can inhibit the elasticity of wire, easy to operate. Filament warp elastic yarns and strong twist yarns also need sizing to restrain shrinkage in order to produce smoothly. The ultimate purpose of sizing is: good pulp shaft, fewer defects, low number of broken ends, high weaving efficiency, improve warp weavability.
The specific requirements are:
(1) Increase the breaking strength of yarn. It is necessary to increase the strength appropriately, but if the excessive pursuit of the increase of sizing strength, it is bound to make the yarn hard and brittle, lose elasticity, but easy to break. The reinforcement rate of pure cotton yarn is generally controlled at 25% ~ 40%, L0% ~ 25%, 10% ~ 20%, >25% of polyester/viscose and pure viscose yarn.
(2) maintain yarn elongation at break. The elongation of the original cotton yarn is generally 7%, and should be kept at 4%-5% after sizing to facilitate weaving, so the elongation reduction rate is ≤30%, polyester/cotton, polyester/viscose yarn ≤25%, pure viscose yarn ≤35%.
(3) improve wear resistance. Because the wear-resisting test has not been standardized at present, the wear-resisting rate of various slurry formulations is also very different.
(4) Hairiness reduction rate. Using YGl7lB yarn hairiness tester and BT 1 2 online hairiness tester, the advanced index of hairiness reduction rate of yarn before and after sizing is more than 75%.
(5) good shaft rate of the weaving shaft. It is required that the sizing yarn is not broken, long, glued, twisted, light pulp wool and pilling, weaving without pulling defects, and the advanced level of good shaft rate is more than 60%.
(6) Number of broken warp of loom. Shuttle loom should be less than 1 thread per (table •h), shuttleless loom should be less than 10 to 15 threads per 100,000 weft.
As a grey cloth for dyeing and finishing, in addition to the requirements of weability, but also easy to desizing, and desizing waste liquid no pollution to the environment. It must be considered in the selection and proportion of slurry.
As a finished cloth, it is required to give the fabric a unique style and feel, and it must be properly adjusted in the types of size, oil agent and sizing rate.